An online leakage alarm system and method for heat exchange tubes in a high-ash and low-temperature flue gas environment

Abstract

The invention discloses an online leakage alarm system and method for a heat exchange tube in a high-ash and low-temperature flue gas environment. The outlet of a first electric valve at a system inlet is connected to one end of a heat exchanger inlet valve via a second electric valve at a system inlet, the other end of the heat exchanger inlet valve is connected to the inlet of a large header at a heat exchanger inlet, the outlet of the large header at the heat exchanger inlet is connected to the inlet of a small header at a module inlet via a module inlet valve, the outlet of the small header at the module inlet is connected to the inlet of a small header at a module outlet via a heat exchange tube, the outlet of the small header at the module outlet is connected to the inlet of a large header at a heat exchanger outlet via a module outlet valve, the outlet of the small header at the module outlet is connected to the inlet of a large header at a heat exchanger outlet via a module outlet valve, the outlet of the large header at a heat exchanger outlet is connected to the outlet of an n-1-level low-pressure heater via the heat exchanger outlet valve, the second electric valve at a system outlet and the first electric valve at a system outlet. The system and method can timely detect leakage of the heat exchange tube.

Description

Technical Field

[0001] The invention belongs to the field of detection technology and relates to an online leakage alarm system and method for a heat exchange tube in a high-ash and low-temperature flue gas environment. Background Art

[0002] Low-temperature heat exchangers are widely used in coal-fired power generation units, mainly to absorb the exhaust heat of flue gas, heat condensate and reduce the coal consumption of the unit. Low-temperature heat exchangers are generally arranged at the inlet of the dust collector. Although the fly ash content in the flue gas is high, it can reduce the flue gas temperature entering the dust collector, thereby improving the dust removal efficiency. At the same time, the flue gas temperature is reduced to below the acid dew point, and SO3 and various metal pollutants can be removed; the exhaust heat absorbed by the low-temperature heat exchanger can also be used to heat the hot water heater, greatly improving the air preheater inlet wind temperature and outlet flue gas temperature, effectively alleviating low-temperature corrosion and ammonium bisulfate ash blockage, so low-temperature heat exchanger technology has been widely used in China. However, due to the variability and poor quality of domestic coal, the received sulfur content, ash content and water content are high, and the ammonia escape in the tail flue gas exceeds the standard, and the flue gas is highly corrosive, resulting in leakage problems in low-temperature heat exchangers after a period of operation.

[0003] The low-temperature heat exchanger is arranged in the flue, which has a large cross-sectional area and contains a lot of fly ash in the flue gas. If the leakage of the heat exchange tube cannot be discovered and handled in time, the leaked condensate will react with the fly ash, causing problems such as fly ash compaction, ash blockage, and corrosion. At the same time, the condensate leaks into the electrostatic precipitator, which will cause a series of problems such as the electrostatic precipitator tripping or clogging the ash removal pipeline.

[0004] Currently, leak detection is mainly carried out through hygrometers. However, due to the high fly ash content in the flue gas, the hygrometer probe is blocked, causing the hygrometer to fail. In addition, the cross-sectional area of ​​the flue is too large, and the hygrometer can only detect the humidity at one point, which cannot effectively solve the problem. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide an online leakage alarm system and method for heat exchange tubes in a high-ash and low-temperature flue gas environment, which can detect leakage of heat exchange tubes in a timely manner.

[0006] To achieve the above-mentioned purpose, the online leakage alarm system for heat exchange tubes in a high-ash and low-temperature flue gas environment of the present invention comprises n-stage low-pressure heaters, wherein a first electric valve at the system inlet, a second electric valve at the system inlet, a second electric valve at the system outlet, a first electric valve at the system outlet and several heat exchangers are arranged between two adjacent stages of the low-pressure heaters, wherein each heat exchanger comprises a heat exchanger inlet valve, a heat exchanger outlet valve, a heat exchanger inlet large header, a heat exchanger outlet large header and several heat exchange modules, wherein each heat exchange module comprises a module inlet valve, a module outlet valve, a module inlet small header, a module outlet small header and several heat exchange tubes;

[0007] The outlet of the n-stage low-pressure heater is connected to the inlet of the n-1-stage low-pressure heater and the inlet of the first electric valve at the system inlet, the outlet of the first electric valve at the system inlet is connected to one end of the heat exchanger inlet valve via the second electric valve at the system inlet, the other end of the heat exchanger inlet valve is connected to the inlet of the heat exchanger inlet large header, the outlet of the heat exchanger inlet large header is connected to the inlet of the module inlet small header via the module inlet valve, the outlet of the module inlet small header is connected to the inlet of the module outlet small header via the heat exchange tube, the outlet of the module outlet small header is connected to the inlet of the heat exchanger outlet large header via the module outlet valve, the outlet of the heat exchanger outlet large header is connected to the outlet of the n-1-stage low-pressure heater via the heat exchanger outlet valve, the system outlet second electric valve and the system outlet first electric valve, and n is a positive integer greater than or equal to 2.

[0008] A heat exchanger local pressure gauge is installed on the heat exchanger outlet large header.

[0009] A module on-site pressure gauge is installed on the module outlet small header.

[0010] The second electric valve at the system inlet is connected to one end of the heat exchanger inlet valve via the system inlet manual valve and the booster pump.

[0011] A system remote pressure transmitter is installed at the outlet of the booster pump.

[0012] The outlet of the heat exchanger outlet header is connected to the outlet of the n-1 stage low-pressure heater via the heat exchanger outlet valve, the system outlet manual valve, the system outlet second electric valve and the system outlet first electric valve.

[0013] The method for online leakage alarm of heat exchange tubes in a high-ash and low-temperature flue gas environment of the present invention comprises the following steps:

[0014] Determine whether the entire system is leaking. When the entire system is leaking, first confirm the leaking heat exchanger, then determine the leaking heat exchange tube by isolating the heat exchange tube, and then isolate the leaking heat exchange tube, while the remaining heat exchange tubes continue to operate.

[0015] The specific steps include:

[0016] 1) System isolation

[0017] Close the first electric valve at the system inlet, the second electric valve at the system inlet, the first electric valve at the system outlet, and the second electric valve at the system outlet, and observe the change in the water side pressure to determine whether the entire system is leaking. If the entire system is leaking, go to step 2);

[0018] 2) Isolation of single heat exchanger

[0019] Open the first electric valve at the system inlet and the second electric valve at the system inlet to restore the water pressure of the heat exchanger, then close all the heat exchanger inlet valves and heat exchanger outlet valves, and judge whether each heat exchanger is leaking according to the change of water pressure in each heat exchanger. If any heat exchanger is found to be leaking, go to step 3);

[0020] 3) Isolation of single heat exchange tube

[0021] Open the heat exchanger inlet valve in the leaking heat exchanger, restore the water pressure of the leaking heat exchanger, close all module inlet valves and module outlet valves in the leaking heat exchanger, and determine whether the heat exchange tube is leaking based on the changes in the water side pressure of each heat exchange tube, and then replace the leaking heat exchange tube.

[0022] The present invention has the following beneficial effects:

[0023] During specific operation, the online leakage alarm system and method for heat exchange tubes in a high-ash and low-temperature flue gas environment described in the present invention finds the leaking heat exchange tube according to the change in the water side pressure of the closed system, isolates the leaking heat exchange tube, and resumes operation of other heat exchange tubes, thereby minimizing the impact of the leakage on the low-temperature heat exchanger system. In addition, a first electric valve at the system inlet and a second electric valve at the system inlet are provided to minimize the risk of internal leakage of the valve. At the same time, the system leak detection can be completed by remote operation, which is convenient and fast, requires low investment, is highly practical, and can quickly detect leaks and handle them.

[0024] Furthermore, a heat exchanger local pressure gauge is installed on the large header at the heat exchanger outlet; and a module local pressure gauge is installed on the small header at the module outlet, which can meet the need for leak detection and reduce costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a system diagram of the present invention;

[0026] Figure 2a It is a working fluid pressure variation curve diagram when the valve does not leak internally and the heat exchange tube 11 does not leak;

[0027] Figure 2b It is a working fluid pressure variation curve diagram when the valve internal leakage is small and the heat exchange tube 11 does not leak;

[0028] Figure 2c It is a working fluid pressure variation curve diagram when the valve internal leakage is large and the heat exchange tube 11 does not leak;

[0029] Figure 2d It is a working fluid pressure variation curve diagram when the valve has no internal leakage and the leakage of the heat exchange tube 11 is small;

[0030] Figure 2eThis is a working fluid pressure variation curve diagram when the valve has no internal leakage and the leakage of the heat exchange tube 11 is relatively large.

[0031] Among them, 1 is the n-level low-pressure heater, 2 is the n-1-level low-pressure heater, 3 is the first electric valve at the system inlet, 4 is the second electric valve at the system inlet, 5 is the manual valve at the system inlet, 6 is the booster pump, 7 is the heat exchanger inlet valve, 8 is the heat exchanger outlet valve, 9 is the heat exchanger inlet large header, 10 is the heat exchanger outlet large header, 11 is the heat exchange tube, 12 is the module inlet small header, 13 is the module outlet small header, 14 is the system outlet manual valve, 15 is the system outlet second electric valve, 16 is the system outlet first electric valve, 17 is the module on-site pressure gauge, 18 is the system remote pressure transmitter, 19 is the heat exchanger on-site pressure gauge, 20 is the module inlet valve, and 21 is the module outlet valve. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0033] refer to Figure 1 The heat exchange tube online leakage alarm system and method under high ash and low temperature flue gas environment of the present invention comprises an n-stage low-pressure heater 1, wherein a system inlet first electric valve 3, a system inlet second electric valve 4, a system inlet manual valve 5, a booster pump 6, a system outlet manual valve 14, a system outlet second electric valve 15, a system outlet first electric valve 16 and a plurality of heat exchangers are arranged between two adjacent low-pressure heaters, wherein each heat exchanger comprises a heat exchanger inlet valve 7, a heat exchanger outlet valve 8, a heat exchanger inlet large header 9, a heat exchanger outlet large header 10 and a plurality of heat exchange modules, wherein each heat exchange module comprises a module inlet valve 20, a module outlet valve 21, a module inlet small header 12, a module outlet small header 13 and a plurality of heat exchange tubes 11;

[0034] The outlet of the n-stage low-pressure heater 1 is connected to the inlet of the n-1-stage low-pressure heater 2 and the inlet of the first electric valve 3 at the system inlet. The outlet of the first electric valve 3 at the system inlet is connected via the second electric valve 4 at the system inlet, the manual valve 5 at the system inlet and the inlet of the booster pump 6. The inlet of the booster pump 6 is connected to one end of the heat exchanger inlet valve 7. The other end of the heat exchanger inlet valve 7 is connected to the inlet of the heat exchanger inlet large header 9. The outlet of the heat exchanger inlet large header 9 is connected to the module inlet small header via the module inlet valve 20. The inlet of the module inlet small manifold 12 is connected, the outlet of the module inlet small manifold 12 is connected to the inlet of the module outlet small manifold 13 through the heat exchange tube 11, the outlet of the module outlet small manifold 13 is connected to the inlet of the heat exchanger outlet large manifold 10 through the module outlet valve 21, the outlet of the heat exchanger outlet large manifold 10 is connected to the outlet of the n-1 stage low-pressure heater 2 through the heat exchanger outlet valve 8, the system outlet manual valve 14, the system outlet second electric valve 15 and the system outlet first electric valve 16, where n is a positive integer greater than or equal to 2.

[0035] A system remote pressure transmitter 18 is installed at the outlet of the booster pump 6 .

[0036] A heat exchanger local pressure gauge 19 is installed on the heat exchanger outlet header 10.

[0037] The module outlet small header 13 is provided with a module on-site pressure gauge 17 .

[0038] The method for online leakage alarm of heat exchange tubes in a high-ash and low-temperature flue gas environment of the present invention comprises the following steps:

[0039] Close the first electric valve 3 at the system inlet, the second electric valve 4 at the system inlet, the first electric valve 16 at the system outlet, and the second electric valve 15 at the system outlet, so that the low-temperature heat exchanger system forms a closed system. Since the working fluid in the system is an incompressible fluid, when the heat exchange tube 11 leaks, the pressure in the system changes. Specifically, according to the change curve of the working fluid pressure, it is judged whether the system is leaking, and at the same time, it is judged whether the first electric valve 3 at the system inlet and the second electric valve 4 at the system inlet have internal leakage. If internal leakage occurs, replace them in time to avoid affecting the leak detection effect.

[0040] When the internal leakage of the first electric valve 3 or the second electric valve 4 at the system inlet is greater than the leakage of the heat exchange tube 11 and the internal leakage of the valve is small, the working fluid pressure change curve is as follows: Figure 2b ;

[0041] When the internal leakage of the first electric valve 3 or the second electric valve 4 at the system inlet is greater than the leakage of the heat exchange tube 11 and the internal leakage of the valve is large, the working fluid pressure change curve is as follows: Figure 2c ;

[0042] When the internal leakage of the first electric valve 3 or the second electric valve 4 at the system inlet is less than the leakage of the heat exchange tube 11 and the leakage of the heat exchange tube 11 is small, the working fluid pressure change curve is as follows: Figure 2d ;

[0043] When the internal leakage of the first electric valve 3 or the second electric valve 4 at the system inlet is less than the leakage of the heat exchange tube 11, and the leakage of the heat exchange tube 11 is large, the working fluid pressure change curve is as follows: Figure 2e .

[0044] When a system leak is found, first determine the leaking heat exchanger, then determine the leaking heat exchange tube 11 by isolating the heat exchange tube 11, and then isolate the leaking heat exchange tube 11, while the remaining heat exchange tubes 11 continue to operate. The specific measures are as follows:

[0045] 1) Isolate the entire system: close the first electric valve 3 at the system inlet, the second electric valve 4 at the system inlet, the first electric valve 16 at the system outlet, and the second electric valve 15 at the system outlet, observe the changes in the water side pressure, and determine whether the entire system is leaking;

[0046] 2) Isolation of single heat exchanger: When the system is isolated as a whole and a leak is found, the isolation operation of the single heat exchanger is performed, the first electric valve 3 and the second electric valve 4 of the system inlet are opened to restore the water pressure of the heat exchanger, and then all the heat exchanger inlet valves 7 and heat exchanger outlet valves 8 are closed. According to the change of the water pressure in the heat exchanger, it is judged whether the heat exchanger is leaking;

[0047] 3) Isolation of a single heat exchange tube 11: After finding the leaking heat exchanger, it is necessary to further find the leaking heat exchange tube 11. Open the heat exchanger inlet valve 7 of the leaking heat exchanger, restore the water pressure of the heat exchanger, close all the module inlet valves 20 and module outlet valves 21 in the leaking heat exchanger, and determine whether the heat exchange tube 11 is leaking based on the change in the water side pressure of each heat exchange tube 11. Repeat the above steps to detect all leaking heat exchangers and mark the leaking heat exchange tube 11;

[0048] 4) System recovery

[0049] Isolate all leaking heat exchange tubes 11, open other valves, and isolate the system as a whole according to step 1). After confirming that there is no leakage, resume the operation of the entire system.

[0050] It should be noted that when the heat exchanger is operating normally, the first electric valve 3 at the system inlet, the second electric valve 4 at the system inlet, the first electric valve 16 at the system outlet, and the second electric valve 15 at the system outlet are closed, so that the low-temperature heat exchanger system forms a closed system. Since the working fluid in the system is an incompressible fluid, if the heat exchange tube 11 leaks, the pressure in the system will change. At this time, according to the change curve of the working fluid pressure, it is judged whether the system is leaking, and at the same time, it is judged whether the first electric valve 3 at the system inlet, the second electric valve 4 at the system inlet, the first electric valve 16 at the system outlet, and the second electric valve 15 at the system outlet have internal leakage. If internal leakage occurs, it should be replaced in time to avoid affecting the leak detection effect. When a system leak is found, the leaking heat exchanger is first judged, and then the leaking heat exchange tube 11 is judged by isolating the heat exchange tube 11, and then the leaking heat exchange tube 11 is isolated, and the remaining heat exchange tubes 11 continue to operate. The present invention has low investment, strong practicality, and can quickly find and handle leaks.

Claims

1. An online leakage alarm system for heat exchange tubes in a high-ash and low-temperature flue gas environment, characterized in that: It comprises n-stage low-pressure heaters (1), wherein a first electric valve (3) at the system inlet, a second electric valve (4) at the system inlet, a second electric valve (15) at the system outlet, a first electric valve (16) at the system outlet and a plurality of heat exchangers are arranged between two adjacent stages of the low-pressure heaters, wherein each heat exchanger comprises a heat exchanger inlet valve (7), a heat exchanger outlet valve (8), a heat exchanger inlet large header (9), a heat exchanger outlet large header (10) and a plurality of heat exchange modules, wherein each heat exchange module comprises a module inlet valve (20), a module outlet valve (21), a module inlet small header (12), a module outlet small header (13) and a plurality of heat exchange tubes (11); The outlet of the n-level low-pressure heater (1) is connected to the inlet of the n-1-level low-pressure heater (2) and the inlet of the first electric valve (3) at the system inlet. The outlet of the first electric valve (3) at the system inlet is connected to one end of the heat exchanger inlet valve (7) via the second electric valve (4) at the system inlet. The other end of the heat exchanger inlet valve (7) is connected to the inlet of the heat exchanger inlet large header (9). The outlet of the heat exchanger inlet large header (9) is connected to the inlet of the module inlet small header (12) via the module inlet valve (20). The outlet of the module inlet small header (12) is connected to the inlet of the module outlet small header (13) via the heat exchange tube (11), the outlet of the module outlet small header (13) is connected to the inlet of the heat exchanger outlet large header (10) via the module outlet valve (21), the outlet of the heat exchanger outlet large header (10) is connected to the outlet of the n-1 stage low-pressure heater (2) via the heat exchanger outlet valve (8), the system outlet second electric valve (15) and the system outlet first electric valve (16), where n is a positive integer greater than or equal to 2; A heat exchanger local pressure gauge (19) is installed on the heat exchanger outlet header (10); The module outlet small header (13) is provided with a module on-site pressure gauge (17).

2. The online leakage alarm system for heat exchange tubes in a high-ash and low-temperature flue gas environment according to claim 1 is characterized in that: The second electric valve (4) at the system inlet is connected to one end of the heat exchanger inlet valve (7) via the system inlet manual valve (5) and the booster pump (6).

3. The online leakage alarm system for heat exchange tubes in a high-ash and low-temperature flue gas environment according to claim 2 is characterized in that: A system remote pressure transmitter (18) is installed at the outlet of the booster pump (6).

4. The online leakage alarm system for heat exchange tubes in a high-ash and low-temperature flue gas environment according to claim 1 is characterized in that: The outlet of the heat exchanger outlet header (10) is connected to the outlet of the n-1 stage low-pressure heater (2) via the heat exchanger outlet valve (8), the system outlet manual valve (14), the system outlet second electric valve (15) and the system outlet first electric valve (16).

5. An online leakage alarm method for heat exchange tubes in a high-ash and low-temperature flue gas environment, characterized in that: The following steps are involved: Determine whether the entire system is leaking. When the entire system is leaking, first confirm the leaking heat exchanger, then determine the leaking heat exchange tube (11) by isolating the heat exchange tube (11), and then isolate the leaking heat exchange tube (11), while the remaining heat exchange tubes (11) continue to operate.

6. The method for online leakage alarm of heat exchange tubes in a high-ash and low-temperature flue gas environment according to claim 5 is characterized in that: The specific steps include: 1) System isolation Close the first electric valve (3) at the system inlet, the second electric valve (4) at the system inlet, the first electric valve (16) at the system outlet, and the second electric valve (15) at the system outlet, and observe the change in the water side pressure to determine whether the entire system is leaking. If the entire system is leaking, go to step 2); 2) Isolation of single heat exchanger Open the first electric valve (3) at the system inlet and the second electric valve (4) at the system inlet to restore the water pressure of the heat exchanger, then close all the heat exchanger inlet valves (7) and heat exchanger outlet valves (8), and judge whether each heat exchanger is leaking according to the change of the water pressure in each heat exchanger. If any heat exchanger is found to be leaking, go to step 3); 3) Isolation of a single heat exchange tube (11) Open the heat exchanger inlet valve (7) in the leaking heat exchanger to restore the water pressure of the leaking heat exchanger, close all module inlet valves (20) and module outlet valves (21) in the leaking heat exchanger, and determine whether the heat exchange tube (11) is leaking based on the change in the water side pressure of each heat exchange tube (11), and then replace the leaking heat exchange tube (11).

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